1. Field of the Invention
The present invention relates generally to redundant fail safe actuators and more particularly to dual or multiple failure operational actuators.
2. Description of the Related Art
Actuators often require redundancy to guarantee reliability even if a failure in the actuator has occurred. For aerospace applications, redundancy in actuators is of prime importance. Actuators presently in use include two motors and a common differential gear box. The gear box represents a single point failure. Failure of the gear box renders the actuator inoperable. There is a need for more reliable actuators that do not contain such single point failures. As will be disclosed below, the present invention provides such redundancy. Although developed for use with the Space Shuttle, the actuator of the present invention has broad based applications.
U.S. Pat. No. 4,215,592, issued to J. A. Calvert, entitled "Redundant Motor Drive System", discloses two motors operating on a common output shaft. It is limited to less than a half revolution and is also limited to two stages. The actuator contains six ball bearings. The failure of any one of these bearings would result in actuator failure. Such a bearing seizure is a major cause of actuator failure. The Calvert system is redundant only with respect to the motors and gear trains, but not with respect to the bearings.